Defense Dept. study finds little risk of Covid spread on planes

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Plane cabin during pandemic
"It's remarkable how safe you are onboard an aircraft," said United CEO Scott Kirby. His airline partnered with the Defense Department on the study. Photo Credit: Shutterstock

The potential for the Covid-19 virus to spread within an aircraft is minimal, according to a newly released Department of Defense study.

Small virus droplets known as aerosols, expelled from a sick passenger, have no more than a 3-in-1,000 chance of reaching the breathing zone of a passenger in the neighboring economy seat, the study's authors found. For passengers in nearby aisles, an average of only one in a thousand aerosols will reach their breathing zone. Both figures assume passengers are wearing masks.

The Defense Department's United States Transportation Command undertook the study in partnership with United and Boeing. United-operated Boeing 767s and 777s were used for the virus simulation.

• Related: Studies chart in-flight transmission of Covid-19 early in the pandemic

To conduct the study, scientists deployed a mannequin equipped with an integrated aerosol generator that was used to simulate coughing and sneezing. The spread of those aerosols was measured using biological sensors that were placed in areas that would be passenger breathing zones during a regular flight operation. The research team undertook 300 tests and did more than 11,500 breathing zone measurements over 46 seats in the planes. Tests were conducted both on the ground and in-flight.

The data, said the authors, "indicates an extremely unlikely aerosol exposure risk for a 12-hour flight."

The findings lend support to the assertion of airlines that planes, aided by their hospital-grade air filters, are an especially safe indoor environment as it relates to Covid-19 transmission. The filters push airborne particles downward. They also recirculate air quickly, with 767s and 777s removing airborne contaminants approximately every two minutes, according to the DOD study  nearly three times as quicky as standard hospital operating rooms.

United CEO Scott Kirby seized on the findings during the company's earnings call Thursday, saying that there is no place indoors that comes close to being as safe as an airplane.

"It's remarkable how safe you are onboard an aircraft," he said.

• Related: No plexiglass on planes, aircraft manufacturers say

The study follows a another study released last week by Boeing that had related findings. After simulating the movement through the cabin of droplets and aerosols from coughs, sneezes and speaking, Boeing concluded that, assuming masks are worn, one foot of separation in an airplane is comparable from a Covid-19 transmission risk standpoint to a conference room with people spaced at least seven feet apart.

Authors of the Defense Department report noted that the study had some limitations. In particular, the study didn't consider the potential for virus transmission through droplets, which are larger than aerosols and are also expelled through coughs, sneezes or speech. The study also assumed that mask wearing in flights is continuous, without interruptions for eating and drinking. Finally, they assumed that the number of Covid-19 positive passengers who get onboard a particular flight will be low.

Not every study on the potential for Covid-19 transmission on commercial flights has yielded such encouraging results. A study published last month in the CDC's Emerging Infectious Diseases journal found that one Covid-19-postive passenger infected 15 other flyers on a March 10 Vietnam Airlines flight from London to Hanoi.

Passengers on that flight, however, were not required to wear masks.

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